This invention relates to overcoated electrophotographic imaging members and more particularly, to electrophotographic imaging members overcoated with a metal acetyl acetonate in an insulating film forming polymer.
The formation and development of electrostatic latent images utilizing electrophotographic imaging members is well known. One of the most widely used processes being xerography as described by Carlson in U.S. Pat. No. 2,297,691. In this process, an electrostatic latent image formed on an electrophotographic imaging member is developed by applying electropscopic toner particles thereto to form a visible toner image corresponding to the electrostatic latent image. Development may be effected by numerous known techniques including cascade development, powder cloud development, magnetic brush development, liquid development and the like. The deposited toner image is normally transferred to a receiving member such as paper.
Electrophotographic imaging systems may utilize single multilayered organic or inorganic photoresponsive devices. In one photoresponsive device, a substrate is overcoated with a hole injecting layer and a hole transport layer. These devices have been found to be very useful in imaging systems. The details of this type of overcoated photoreceptor are fully disclosed, for example, in U.S. Pat. No. 4,265,990. The entire disclosure of this patent is incorporated herein by reference. If desired, multilayered photoresponsive devices may be overcoated with a protective layer. Other photoreceptors that may utilize protective overcoatings include inorganic photoreceptors such as the selenium alloy photoreceptors, disclosed in U.S. Pat. No. 3,312,548, the entire disclosure of which is incorporated herein by reference.
When utilizing such an organic or inorganic photoresponsive device in different imaging systems, various environmental conditions detrimental to the performance and life of the photoreceptor from both a physical and chemical contamination viewpoint can be encountered. For example, organic amines, mercury vapor, human fingerprints, high temperatures and the like can cause crystallization of amorphous selenium photoreceptors thereby resulting in undesirable copy quality and image deletion. Further, physical damage such as scratches on both organic and inorganic photoresponsive devices can result in unwanted printout on the final copy. In addition, organic photoresponsive devices sensitive to oxidation amplified by electric charging devices can experience reduced useful life in a machine environment.
Photoreceptors overcoated with insulating polymers tend to exhibit a build-up in residual potential during cycling because all of the charges initially deposited during uniform charging cannot not be fully dissipated upon exposure to light. This phenomenon is manifested by an increase in background deposits in the final xerographic copy. Thus, abrasion-resistant and transparent polymers such as polycarbonates, polyesters, polymethacrylates, polysulfones, polyarylates, polyimides, etc. are generally too highly resistive for use in overcoats for photoreceptors that are cycled. Attempts have been made to add other materials to address the residual potential problem. Unfortunately, properties, such as transparency, of the overcoating layer may be adversely affected by the addition of such added material. More specifically, the transparency of an overcoating layer may become translucent or even opaque. Further, some additives detract from the mechanical properties of an overcoating and affect, for example, adhesion between the overcoating and the underlying layer.
Conductive additives have been incorporated into overcoating layers to reduce residual potential build up during cycling. However, some additives such as ammonium salts tend to increase lateral conductivity, particularly under ambient high humidity conditions. Lateral conductivity can cause blurring of the edges of the image or even total loss of the image in the final copy.
An overcoating layer is described in U.K. No. 2,106,659. This overcoating layer requires the use of a blocking layer. The requirement of an additional coating step complicates the fabrication of the photoreceptor, can cause delamination, increases residual potential, and reduces sensitivity.